Joint Surface Replacement System

ABSTRACT

The present invention relates to an articular joint replacement system. The system has first and second components. Each component has a tapered head piece for covering the end of a bone and for acting as an articular surface, an integrally formed screw stem having a length sufficient to extend into the medullary canal, and inwardly angled bone grips affixed to the underside of the head piece to allow solid fixation to the bone by compression press fit. The head piece of the first component is provided with a shaped exterior surface which complements the shaped exterior surface of the head piece of the second component and which allows motion in three planes.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to apparatus, systems and methods forreplacing and/or repairing cartilaginous surfaces in a human joint.

2. Description of Related Art

The use of prosthetic devices to replace joints and various bone andcartilage structures in a human body is well known in the prior art.These devices have taken a wide variety of configurations and shapeswhich are often closely related to the particular joint or anatomicalstructure being replaced. Described below are some of various devicesshown in the patent literature.

U.S. Pat. No. 3,681,786 to Lynch, U.S. Pat. No. 4,725,280 to Laure, U.S.Pat. No. 4,759,768 to Hermann et al., U.S. Pat. No. 4,955,916 toCarignan et al., and U.S. Pat. No. 5,007,932 to Bekki et al. discloseprosthetic devices designed to replace human finger joints. These jointreplacement devices include both single component apparatus andmulti-component apparatus.

For instance, Lynch discloses a one-piece prosthesis formed from asingle piece of flexible elastomeric, physiologically inert material anda polyester felt pad embedded within the prothesis. The felt pad has anexposed surface which provides for the ingrowth of body tissue. Laurediscloses a prosthetic joint having a shell-like member secured to thedistal end of one phalanx and a tack portion which extend into the otherphalanx for replacement of either the proximal or distal phalangealjoint of the finger.

Hermann discloses a prosthetic joint comprising two pins witharticulation surfaces provided between the pins, whereby the pins aredesigned to be directly or indirectly inserted into a respective one ofthe two bones to be joined. The Carignan discloses a thumb jointprosthesis having tapered and threaded carpal and metacarpal components,whereby the carpal component has a U-shaped cavity containing apolyethylene insert that receives a tapered head received in acorresponding cavity within the metacarpal component. Bekki discloses atwo-member prosthetic device where the first member has a convex curvedsurface and the second member has a concave curved surface which is insliding contact with the convex curved surface.

Various patent literature is also directed to prosthetic devicesdesigned to replace other human joints, such as, elbows, knees, toejoints, and the like. For instance, U.S. Pat. No. 2,696,817 to Prevodiscloses a prosthetic elbow joint comprising two finned shaftsinsertable into the marrow cavities of the humerus and the ulna, whichshafts are pivotally connected by a trunnion.

U.S. Pat. No. 4,355,429 to Mittlemeier et al., U.S. Pat. No. 4,462,120to Rambert et al., U.S. Pat. No. 4,085,466 to Goodfellow et al. and U.S.Pat. No. 5,176,710 to Hahn et al. are directed to various kneeprosthetic devices. Mittlemeier discloses a slide prothesis whichincludes a surface replacement for the knee cap having anchoring pinsthat are provided with a saw tooth-like or bone screw-shaped profile.Rambert discloses a total knee prosthesis having upper and lower supportmembers provided with externally threaded, tapered shanks to which theyare detachably secured, whereby the shanks are screwable into themedullary canals of the femur and the tibia. Goodfellow discloses adevice having first and second components respectively providing convexand relatively flat articulatory bearing surfaces. Hahn discloses aprosthetic device made from materials having a low bulk modulus ofelasticity.

Toe joint replacement systems have also been disclosed in the prior art.For instance, U.S. Pat. No. 4,642,122, to Steffee and U.S. Pat. No.5,037,440 to Koening disclose devices for replacing a toe joint. TheSteffee device comprises a one-piece tack member implantable into thedistal end of a metatarsal and a one-piece socket member implantableinto the proximal end of a phalanx. The tack member has an enlarged headdefining a part-spherical convex surface which engages a part-sphericalconcave bearing surface on an enlarged head of the socket member. Koenigdiscloses a device that also includes a first member having a convexsurface and a second member having a concave surface.

In addition to the patent literature, various commercial toe implantsare currently on the market however many of these commercially availableimplants deteriorate, collapse, break and Suffer torque deformation.Additionally, implantation of some devices require modifications to thesub-chondral bone. Still further, some devices require the use ofsilicone, silastics, glues, ingrowth jackets, and grommets. Thesedisadvantages are overcome by the joint replacement apparatus, systemsand methods of the present invention.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide animproved joint surface replacement apparatus, system and methods.

It is a further object of the present invention to provide a jointsurface replacement system that eliminates breakage, bulk and excessiveweight—the major contributory factors which lead to destructive lateralshearing forces resulting in complete implant failure.

It is a further object of the present invention to provide a jointsurface replacement system as above that provides a full range of motionin three planes.

It is still a further object of the present invention to provide a jointsurface replacement system as above which is firmly anchored to bone.

It is yet a further object of the present invention to provide arelatively simple method for installing the joint surface replacementsystem of the present invention making it extremely cost effective.

The foregoing objects are achieved by the joint surface replacementsystem and the installation method of the present invention.

In accordance with the present invention, the joint surface replacementsystem of the present invention has two elements which are eachimplanted into one of the bones forming the joint. The two elementsdefine the new joint surfaces. A first one of the elements has apartially spherical member for covering an end of a first one of thebones, a centrally located screw means formed integrally with thepartially spherical member and a means for gripping the end of the firstbone for allowing solid fixation by compression press fit. The secondone of the elements has a structure substantially identical to that ofthe first one of the elements. It too has a partially spherical memberfor covering an end of the second bone, an integral screw means and abone end gripping means. The second element differs from the firstelement only by the shape of the partially spherical member. The secondelement has a partially spherical member with an outer surface shaped tomate with the outer surface of the partially spherical member of thefirst element. In a preferred embodiment, the first element has apartially spherical member with a convexly shaped outer surface, whilethe second element has a partially spherical member with a concavelyshaped outer surface.

It has been found that the joint surface replacement system of thepresent invention offers numerous advantages. For example, the jointsurface replacement system is formed from low-mass components whicheliminates breakage, bulk and excessive weight. The joint surfacereplacement system replaces only the area of anatomic cartilage by sizeand function and provides full range of motion in all three planes. Thejoint surface replacement system also completely eliminates detriticsynovitis.

Other details of the joint surface replacement system of the presentinvention as well as other objects and advantages attendant thereto areset forth in the following detailed description and the accompanyingdrawings in which like reference numbers depict like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel and the elementscharacteristic of the invention are set forth with particularity in theappended claims. The figures are for illustration purposes only and arenot drawn to scale. The invention itself, however, both as toorganization and method of operation, may best be understood byreference to the detailed description which follows taken in conjunctionwith the accompanying drawings in which:

FIG. 1 illustrates a dorsal-plantar view of a human foot showing a totalfirst metatarsal phalangeal joint articular surface replacement usingthe joint surface replacement system of the present invention.

FIG. 2 illustrates a sagittal view of the foot of FIG. 1 showing thejoint surface replacement system of the present invention.

FIG. 3A illustrates a side view of a first component of the jointsurface replacement system of the present invention.

FIG. 3B illustrates an end view of the first component of FIG. 3A.

FIG. 4A illustrates a side view of a second component of the jointsurface replacement system of the present invention.

FIG. 4B illustrates an end view of the first component of FIG. 4A.

FIG. 5 illustrates a side perspective view of a screw component inaccordance with one or more embodiments of the present invention.

FIG. 6 illustrates a side perspective view of another screw component ofthe present joint surface replacement systems.

FIGS. 7A-8D are various views of the screw component of FIG. 5 inaccordance with various embodiments of the invention.

FIGS. 9A-9D illustrate details of the screw components in accordancewith various embodiments of the invention.

FIGS. 10A-10C illustrate various perspective views of a reamer tool usedfor application of the screw components of the invention.

FIG. 11 illustrates the various sizes the first and second screwcomponents of the invention may be provided with depending uponapplication thereof.

FIGS. 12A-13B illustrate different perspective views of the other screwcomponents in accordance with various other embodiments of theinvention.

FIGS. 14A-14C illustrate various perspective views of a reamer toolsuitable for use with the screw components shown in FIGS. 12A-13B.

FIG. 15 illustrates different reamer tools and first and second screwcomponents in accordance with various embodiments of the invention.

FIGS. 16A-16B illustrate different screw components in accordance withembodiments of the invention.

FIG. 17 illustrates different subchondral bone replacement apparatus ofvarious embodiments of the invention.

FIG. 18 illustrates a sagittal view of a foot showing the joint surfacereplacement system including the screws and subchondral bone replacementapparatus in accordance with one or more embodiments of the invention.FIG. 18 illustrates a sagittal view of a foot showing the joint surfacereplacement system including the screws and subchondral bone replacementapparatus in accordance with one or more embodiments of the invention.

FIGS. 19A-19DB illustrate different top down views of the installationof the present screws (FIGS. 19B and 19D) and bottom up views of thesaid screws (FIGS. 19A and 19C) showing expandable tri-prong stemfixation anchor of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In describing the preferred embodiment of the present invention,reference will be made herein to FIGS. 1-19D of the drawings in whichlike numerals refer to like features of the invention.

In describing the instant invention, reference is made herein to U.S.Pat. No. 5,683,466 describing clockwise rotational spikes, the entiretyof which is incorporated herein by reference. The instant apparatus,systems and methods are directed to subchondral bone restructure and/orreplacement. The various implant screws disclosed herein, and describedin relation to FIGS. 1-18, each have anti-rotation bone grips on asurface thereof for fixation to provide increased stability andanti-rotation once secured into bone. Additional improvements of theinstant screws that provide ridged fixation and improved stabilityresulting in anti-rotation of the screws once within the bone include,but are not limited to: scalloped underside protrusions of the screw;curved radius edge; v-shaped bone contact side; threaded or non-threadedexpandable tri-prong stem fixation anchor; counterclockwise positionedgripping protrusions; angled or curved threads on the screw stem; athreaded counter-bore; a subchondral bone growth disc residing at theunderside of the screw; a subchondral bone growth coating on the screwand/or screw stem surfaces; and combinations thereof.

Referring now to the drawings, FIGS. 1 and 2 illustrate a total firstmetatarsal phalangeal articular surface replacement using one or morejoint surface replacement apparatus, systems and methods of theinvention. In accordance with one or more embodiments, various jointsurface replacement systems 10 of the invention are shown. These systemsinclude a first component 12 implanted into a first bone 14 and a secondcomponent 16 implanted into a second bone 18. The implant components 12,14 and system 10 replaces only cartilaginous surface areas andfacilitates functioning to the original anatomic structures.

Referring to FIGS. 3A-3B, the first component 12 is a single-bodystructure having a partially spherical, tapered head piece 20 forcovering the bone and functioning as an articular surface. Thesingle-body structure also includes an integrally formed cancellousscrew stem 22 and a plurality of anti-rotation locking bone grips 24integrally formed on the interior side 26 of the head piece 20. Theinterior surface 26 and the exterior surface 28 of the head piece areeach preferably convexly shaped. In one or more embodiments the twosurfaces 26, 28 may have different radii so as to form a tapered headpiece with the thinnest portion being at the outer periphery of thehead. While not meant to be limiting, as an exemplary first component 12of the invention the center of the head piece may have a thickness ofabout 2.0 mm while the outer periphery has a thickness of about 1.0 mm.The screw stem 22 is preferably centrally located with respect to thehead piece 20.

Referring to FIG. 3A, the screw stem 22 has a non-threaded head portion30 and a tapered threaded portion 32. The threaded portion has a lengthL sufficient to allow the first component to be inserted through thesub-chondral bone and into the medullary canal so as to substantiallyeliminate implant pistoning. Typically the length L will be from about 5to about 15 millimeters. The non-threaded head portion 30 typically willhave a length of about 3.5 millimeters. The thread on the portion 32 mayhave any suitable thread pattern and any suitable pitch.

The head piece 20 may be provided with a centrally located geometricshaped bore 34 at the top exterior surface 28 thereof. In one or moreembodiments the bore 34 may be a hexagonally shaped, tapered bore 34. Areamer tool 100 of the invention, as shown in FIGS. 10A-10C, 14A-14C and15, includes a mating protrusion at an end thereof that fits into thebore 34 opening for installing and removing the first component into andfrom bone. The head piece 20 is dimensioned to allow it to fully coverthe end of the bone in which it is inserted.

Referring to the drawings, the plurality of anti-rotation locking bonegrips 24 are radially spaced around and on the interior side 26 of thehead piece 20. In accordance with one or more embodiments, theanti-rotation locking bone grips 24 may include a plurality ofcounterclockwise positioned gripping protrusions 124 (see, e.g., FIGS.3B and 4B), a plurality of scalloped edges 224 (see, e.g., FIGS. 5-8C),inwardly angled grooved and scalloped bone grips 324 (see, e.g., FIGS.12A-13B), angled or curved threads 400 on the screw stem (see, e.g.,FIGS. 5-9C and 12A-13B), or any combination thereof.

As an alternative as shown in FIG. 3A, the bone grips may be angledinwardly in relationship to the threads 400 of the screw stem. Theinwardly angled bone grips allow solid fixation by a compression pressfit, thereby eliminating lateral stress forces in the transverse planeand rotational forces in the frontal plane. Preferably each bone griphas a length of about 2.0 mm.

Referring to FIG. 3B, the instant bone grips 24 may includecounterclockwise positioned anti-rotation hook-shaped bone grippingprotrusions 124 that are radially spaced about the center 36 of the headpiece 20. Each of these bone gripping protrusions 124 may be spacedwithin the inner two-thirds of the bone in which the component is to beimplanted, preferably from about 3 to about 4 mm from the center 36. Thenumber of bone counterclockwise bone gripping protrusions 124 residingon the interior side 26 of the head piece 20 may vary depending upon thesize of the first component implant 12 and/or the bone into which it isbeing inserted. It should also be appreciated that the placement ofthese counterclockwise bone gripping protrusions 124 may vary, and maybe located at various positions on the interior side 36 including, forinstance, equidistant from one another, in a circular pattern, in offsetnon-circular patterns, in rows or columns, and the like.

As shown in FIGS. 4A-4B, the second component 16 may also include aplurality of anti-rotation locking bone grips 44 radially spaced aroundand on the interior side 40 thereof. The second component 16 has auni-body (single bod) construction with a partially spherical, taperedhead piece 40, a centrally positioned cancellous screw 42 and aplurality of locking bone grips 44 radially spaced around and on theinterior side 46 of the head piece 40. The head piece 40 differs fromthe head piece 34 of the first component 12 only by its shape. As shownin FIGS. 4A-4B, the head piece 40 has concavely shaped interior andexterior surfaces 46 and 50 respectively so as to allow the head piece40 to mate with the head piece 34 and provide motion in all threeplanes. As before, the inner and outer surfaces 46 and 50 are formed bydifferent radii so as to form a tapered construction having its thinnestportion at its outer periphery.

In one or more other embodiments the anti-rotation locking bone grips ofthe invention may include a plurality of scalloped edges 224 residingalong a periphery of the interior side 26 of the head piece 20 of firstcomponent 12, and/or along a periphery of the interior side 46 of thehead piece 40 of second component 16. FIGS. 5 and 6 show different sideperspective views of various first component parts 12 of the inventionhaving scalloped edges 224. These serrated and/or scalloped ridges/edges224 at the interior side 26 of the head piece 20 of the screw preventscrew rotation.

The various perspective views of FIGS. 7A-8D show more details of thescalloped edges 224. These scalloped edges 224 may be serrated ornon-serrated to prevent rotation once within the bone. In one or moreembodiments the scalloped edges 224 may be serrated scalloped edges thatfixate into the bone upon rotation and insertion of the screw into bone(via reamer tool 100) to provide a secure and non-rotatable screw withinthe bone. These serrated scalloped bone grip edges may be angledcounterclockwise to further prevent counterclockwise rotation that maypotentially undesirably loosen the joint surface replacement system. Theserrated scalloped bone grip edges 224 reside entirely around the edgesof the screw cap surface at edges thereof (e.g., 360-degrees) to a depthranging from about 0.5 mm to about 1 mm deep. In certain embodiments theserrated scalloped bone grip edges 224 may be used at certain locationsand based on indications of bone conditions.

Referring to FIGS. 9A-9D various detailed angles and features of theinstant screws 12, 16 are shown. FIG. 9A depicts the curvature of theinwardly sloped threads 400 of the screw stem, along with the anglesthereof, while FIG. 9B shows the stem along line A-A′ in FIG. 9A. Theexploded view sections “C” and “B” are further depicted in FIGS. 9C and9D, respectively. Referring to FIG. 9D, the entire outer peripheralradius edge of the screw head (i.e., the entire 360-degrees thereof) mayhave 90-degree curved sharp edges that engage subchondral bone uponaffixing and tightening the screw therein. These 90-degree curved sharpedges hold the instant joint surface replacement firmly into thesubchondral bone with improved and increased stability to preventlateral shear and weight bearing forces from jarring the screw loose. Italso transfers these forces off of the threaded screw stem, therebypreventing the threaded stem from loosening or backing out from counterrotation. Furthermore, downwardly extending 90-degree curved sharp edgesprevent any articular interference of the instant subchondral bonereplacement allowing it to function efficiently and withoutcomplications.

FIGS. 12A-14C show alternate embodiments of the instant screws having aplurality of anti-rotation locking bone grips. As shown theanti-rotation bone grips may comprise a plurality of grooved, scallopedchannels 324 that allow for bone ingrowth to grow therein. While thedrawings depict the instant grooved, scalloped channels 324 on screw 12,it should be appreciated that like grooved, scalloped channels 344 maybe provided on the opposing or mating screw 16. These grooved, scallopedchannels 324 may have different shapes and sizes as shown in FIGS. 13Aand 13B. They also may reside at various locations along and around thesurface of the head portion 20, 40 of the instant screws. By allowingbone ingrowth to occur within these grooved, scalloped channels 324, theoccurrence of counter rotation or backing out of the threaded stem ofthe implant (i.e., “loosening of the screw”) is drastically reduced ascompared to the clockwise rotational spikes. The grooved, scallopedchannels 324 of the invention provide improved rigid fixation.

While the various plurality of anti-rotation bone grips (i.e., 124/144,224/244, 324/344) are described herein with respect to each other, itshould be appreciated that the instant screws 12, 16 may be providedwith any combination thereof. For instance, FIG. 2 shows screw 12 havingscalloped edges 224, while screw 16 has counterclockwise protrusions144. It should also be understood that a single screw 12 or 16 may havea combination of the instant anti-rotation bone grips (i.e., 124/144,224/244, 324/344) provided on surfaces thereof for additionalanti-rotation or prevention of screw loosening.

Referring to FIG. 11, the present screw components 12, 16 may beprovided with a variety of different dimensions suitable for intendedpurposes. The components 12 and 16 may also be interchangeable, and arepreferably formed from low-mass materials. For example, the componentsmay be formed from chromium alloys such as a chromium cobalt alloy,titanium, a titanium alloy or stainless steel. The use of thesematerials eliminates breakage, bulk and excessive weight—majorcontributory factors to increased lateral shearing forces, the leadingcause of decreased longevity and failure.

In a preferred embodiment of the present invention, the interiorsurfaces 24 and 46 of the head pieces 20 and 40 are coarsely finished toallow for boney ingrowth and to facilitate fixation. Additionally, eachof the bone grips 24 and 44 are provided with coarse surfaces which alsoallow for bone ingrowth and to facilitate fixation to the bone.

In one or more embodiments of the invention, each screw stem may beprovided with angled or sloped cancellous threads 400 ranging in sizefrom about 1.5 mm to about 7.5 mm. It should be appreciated that thesize will vary depending upon the joint application for various sizedjoints. The angled cancellous threads may be provided at both sides ofthe joint when necessary. The barrel of the screw stem may have a barrelthat is angled at about 10 degrees and fully threaded. The screws alsoprovide increase stability in view of the widening thereof and threadedcounter-bore.

The thickness of the instant “joint surface replacement” implant systemmay be about 1 mm, and even up to about 3 mm thick. In certainembodiments an optimal thickness of about 2-4 mm may be requireddepending on surface materials needed for a total joint replacement orincreased strength to all implants including HEMI implants. Thisadditional or optional thickness is essential to bone lengthening, forcorrection of short first metatarsal or proximal phalanx. It may be inboth the metatarsal and/or phalangeal components.

In one or more embodiments, the subchondral bone replacement systems andmethods of the invention are non-weight bearing since the screws may beup to 20% smaller than outer circumference. The instant screw components12, 16 may be composed of any material known to be used for joint“surface” replacement including, but not limited to, polyethylene,ethylene, polyurethane, polypropylene and other hard plastics, ceramics,titanium, cobalt chromium, stainless steel, SS 17-4ph hardened, and thelike.

In certain embodiments, an optional two-piece joint replacement isprovided, which may include a screw anchor a snap-on articular surfaceimplant. Various embodiments of the invention provides an optionalcannulated implant, as well as a hexalobe/torx drive with recessedand/or chamfered edges

FIGS. 19B and 19D illustrate different top down views of theinstallation of the present screws using reamer tools 100 of theinvention. FIGS. 19A and 19C illustrate bottom up views of the variousscrew components 12, 16 of the invention having threaded (ornon-threaded) expandable tri-prong stem fixation anchor of theinvention.

Also shown in FIGS. 7C-7D and 8C-8D is a non-tapered hexagonally shapedbore 300 centrally located on the exterior surface 28 of the head piece20 (e.g., a hexagonally shaped, non-tapered bore as shown in FIGS. 7Dand 8D). In these embodiments the reamer tool 100 has a hexagonallyshaped drive portion to fit into the hexagonally shaped bore forsecuring and locking the screw into bone via the anti-rotation grips.

While the centrally located bore is shown as a hexagonally shaped,non-tapered bore, it should be appreciated that the screw bores may beinternally tapered or non-tapered with a variety of different geometricconfigurations. For instance, the driver hole configurations and methodsmay be altered to be configured as a star shaped bore that accommodatesa star shaped driver of a reamer tool 100. It has been found that thestar shaped drive allows greater driver engagement, which in turn,minimizes slippage of the star shaped driver for screw insertion intobone, particularly size T10 or T15. The edges of the driver hole mayalso be rounded to eliminate potential interference with articular rangeof motion.

Still further, a cap cover may be provided for the driver hole. The capcover may be a press fit cap cover. The driver hole cap cover preventssoft tissue and material build up within the driver hole. In one or moreother embodiments the cap cover may be anywhere from 1-4 mm to maintainlength of the bone. The cap cover may be a screw cap cover having athickness from about 1 mm to 4 mm at the edge thereof.

Referring to FIGS. 17 and 18, the present apparatus, systems and methodsalso include a subchondral bone replacement growth component. In one ormore embodiments, the subchondral bone replacement growth component maybe provided as a bone growth disc 200 (see, e.g., FIGS. 17 and 18), bonegrowth coating 201 (see, e.g., FIG. 18), or any other type ofsubchondral bone replacement growth apparatus.

In one or more embodiments the subchondral bone replacement may be inthe form of a disc for insertion into an opening drilling in the bone.In other embodiments the subchondral bone growth replacement is a layerof a suitable material that coats the surface of the screw stem, thethreads of the stem, the underside of the screw head, and/or any of theinstant anti-rotation bone grips of the invention. One or more bonein-growth coatings may be applied to the entire screw and/or screw stemto provide improved and increased rigid fixation of the screw stem tobone via bone in-growth coating capabilities. The bone in-growth coatingon the screw and/or screw stem increases the rigidity of the screwfixation and minimizes counterclockwise rotation that may potentiallyloosen the joint surface replacement system in all applications andjoints.

These subchondral bone replacement systems and methods may be conjoinedto the undersurface of all joint replacement systems and insertedtogether. For instance, the subchondral bone replacements are suitablefor use when subchondral bone has been worn or destroyed by thearthritic process. The ability to replace this lost zone of subchondralbone will be beneficial for proper joint function and implant longevity,as well as provide shock absorption, increase bone length, and providesupport to the instant joint replacement implants of the invention.

Referring to FIGS. 17 and 18, in one or more embodiments the subchondralbone replacement is a bone growth disc 200 added under the screws of theinvention. In use, a bone and/or joint in need of repair is drilled outto a predetermined depth that accommodates both the screws of theinvention and the subchondral bone replacement (e.g., subchondral bonereplacement disc) placed under the screw. The subchondral bonereplacement may be a part of or attached to the screw, or it may beseparate therefrom. A portion of the bone material is removed, thesubchondral bone replacement (e.g., subchondral bone replacement disc)is positioned in the drilled opening in the bone, followed by securingthe screws of the invention therein. Again, the screw may have the bonegrowth disc on it. The method and system replace subchondral bone withthe disc. In certain embodiments the subchondral bone replacementmaterial may be provided in the opening in the bone and need to hardenbefore inserting the screw therein. A preferred subchondral bonereplacement may be a biological bone growth formulation. Synthetic bonegrowth formulations may also be used.

When the subchondral bone replacement is in the form of a disc, suchdisc may be about 3 mm to 5 mm thick. It will be a measured, formed,cannulated piece of hard, porous, synthetic bone as described, that willbe manufactured, supplied and fitted underneath each sized implant, bydiameter and radius when needed. The worn area of subchondral bone willbe either cut flat or reamed in accordance to the proper radius of theimplant. Depending on the amount of subchondral bone depth that has beendestroyed, will depend the amount of depth or thickness needed toreplace and order to fit the individual circumstance and implant. Itwill then be installed underneath and together with the implant, in onestep. Over time, bony in growth (osteoconductivity) will take place intothis biocompatible synthetic material. Thickness/depth range for thisreplacement can be from 2 mm to 8 mm.

Materials suitable for use in the present subchondral bone replacementsystems and methods have the ability to replicate and/or function assubchondral bone does, such that, it is able to act as bumper system(shock absorbing portion of the bone) that is highly significant tonormal joint function. These materials also have the ability for theneeded bone in-growth coatings to grow within the porous material usedto replace the subchondral bone. The subchondral bone replacementsystems and methods may be used in combination with any of the abovesystems and methods of the invention. The subchondral bone replacementmay be composed of a filler material of a calcium phosphate cementformulation that provides osteoconductivity, biocompatibility, andexcellent baseline strength.

The instant subchondral bone replacement systems are particularlysuitable for loss of the cartilage zone due to destruction caused byarthritis. Calcium Phosphate and many other forms of porous, syntheticbone materials that are used for this purpose, act to fill “voids”, andare made of proprietary formulations that provide “osteo-conductivity,biocompatability and excellent baseline strength.

Other embodiments of the invention are directed to altering the radiusedges of joint surfaces replacements. Curved edges are added on theentire radius of all joint surface replacements to engage into thesubchondral bone. These curved edges provide improved and increasedstability and rigid fixation of the joint surface replacements to thesubchondral bone, as well as resist weight bearing forces and forcespotentially loosening the screw stem. The curved edges of the jointsurfaces replacements also eliminate potential interference witharticular range of motion.

Referring to FIGS. 10A-10C, 14A-14C, and 15, the invention is alsodirected to in one or more embodiments reamer tools 100 for use with thevarious screws and driver hole configurations of the invention. Aone-piece reamer tool instrument may be provided that combines thecountersink instrument to the existing drill bit and surface grinder forenabling a single step process (rather than a two-step process) ofprepping the end of the bone and for inserting all joint surfacereplacements, all within a single step. Referring to FIGS. 14A-14B, thereamer tools 100 include blades having staged double blades that enablesthe countersink and surface grind in a single step. The instruments mayalso include a star shaped driver instrument mounted at the oppositeend, rather than using a separate hand standard hexagonally shapeddriver, allowing significantly improved purchase power and minimizingslippage when inserting all joint replacement systems. The star shapeddriver also provides the option for both power drive and handinstallation, which is preferred in one or more embodiments. Theone-piece instruments of the invention also save or decrease significantsurgical time.

In accordance with one or more embodiments of the invention, the jointsurface replacement system of the present invention may be installed byone or more of the following steps. It should be appreciated that otherinstallation methods are also envisioned within the scope of the presentinvention.

A. Performing the standard surgical approach for arthroplasty to theinvolved joint to be replaced through skin, superficial and deep tissuespreserving vital structures and tendons;

B. Entering capsular structures through the usual incisional approach,as to expose the involved joint surfaces for replacement;

C. Performing the standard peripheral “Chielectomy” procedure whenappropriate or indicated, preserving the dorsal sack and all subchondralbone;

D. Prepping subchondral bone and worn joint surfaces with a mirror imagedrill bit, containing a central guide hole drill bit to maintainposition while drilling. Marking the centermost portion of the jointsurface and placing a guide hole bit on the marked central area andbeginning drilling until the entire bore just approaches joint surfaceand “mildly scouring” worn joint surface until evenly and shaped withthe bore bit;

E. Drilling guide hole (length times width) to appropriate size of stemof implant, and optionally drilling out additional space for subchondralbone replacement disc;

F. Counter sinking subchondral bone and at guide hole site, for theseating of the screw head barrel;

G. Tapping guide hole for thread size of implant stem;

H. Grasping the unibody articular surface replacement unit with forcepsand placing screw stem (and optionally subchondral bone replacementdisc) into tapped guide hole of bone. Utilizing reamer tool 100, screwin entire articular surface replacement into subchondral bone. Bothscrewhead barrel and anti-rotation bone grips engage snugly intosubchondral bone during final quarter to half compression turns ofinsertion, and then turn counterclockwise to lock in anti-rotation bonegrips;

I. Flushing entire wound with appropriate antibiotic flush;

J. Approximate and close capsule, deep tissues and superficial tissuesin layers with absorbable sutures. At this point, optional tendonlengthening or transfers may be performed when indicated;

K. Closing skin in the usual fashion and apply post-operative dressing;and

L. Maintaining early post-operative range of motion exercise andimmediate ambulation after first three days.

The articular surface replacement is designed to further press fit andcompress as weight bearing in normal activity continues post-operativelyand throughout life.

The various joint surface replacement systems of the invention replaceonly the function of cartilage, not the function of a metatarsal,phalangeal, femoral or humeral head. The partially spherical shape tothe head pieces serves to replace the area of anatomic cartilage by sizeand function. The angled thread, cancellous screw stem of each componenteliminates pistoning forces and wearing of the inner cortical wall whichleads to slippage and failure. The screw stem also allows easy removalwhen indicated and provides reliable stability and compression.

The taper to the outer spherical screw head barrel allows each componentto be anchored to the bone via insertion and joint use compression overtime to press fit into bone. It also eliminates lateral shearing forcesin both the transverse and sagittal planes, thus relieving the entirescrew stem form abnormal forces. The angled bone grips are designed atthe same thread angle to engage sub-chondral bone during the lastone-quarter turn of compression fit during insertion of each component.The bone grips further anchor the respective component to bone duringjoint use while weight bearing.

The joint surface replacement systems of the present invention areeasily and clearly viewed on radiographs for observation and follow-up.The uni-body design of the system components allows a total view of theposition of the entire implant.

The joint surface replacement systems are advantageous as thesub-chondral bone is left intact, thereby maintaining length and jointfunction of shock absorption and proprioception. Additionally, symmetryis preserved to that of the contralateral side. With respect to softtissues, periarticular tendon, capsule and ligamentous structures areleft intact during implantation of the system of the present invention.Soft tissue release and/or tendon transfer is utilized for jointalignment only, not for insertion of the implant articular replacement.Still further, the dorsal synovial sac may be preserved.

The system of the present invention eliminates detritic synovitis. Nosilicone, no silastics, no glues, no ingrowth jackets and no grommets,which cause abrasion shards are required. Additionally, there is noshearing fractures of the stem or articular surface materials. Stillfurther, encapsulations of microfragments, bone erosions and fibrosisare eliminated, unlike other implants.

The articular surface replacement system of the present invention may beinserted at time of an osteotomy and may be used for primary orsecondary fixation of a head osteotomy. It eliminates the need to healthe first osteotomy before performing the implantation procedure.

If desired, the head pieces of the components may be fabricated from amaterial different from the material used for the screw stem and thebone grips. For example, they may be fabricated from ceramic materialsor high density polyethylene for situations where a hemi-joint orpartial joint implantation is to be performed. A hemi joint procedurewould be performed where replacement of one articular surface alone isindicated. A partial joint procedure may be performed where only wornareas are to be replaced.

While the joint surface replacement system has been described in thecontext of replacing metatarsal phalangeal joints, it should berecognized that the same system could be used to replace other joints.For example, the system could be used to replace large joints such aships and shoulders and digital joints of the fingers and toes.

It is apparent that there has been provided in accordance with thisinvention a joint surface replacement system which fully satisfies theobjects, means and advantages set forth hereinbefore. While theinvention has been described in combination with specific embodimentsthereof, it is evident that many alternatives, modifications andvariations will be apparent to those skilled in the art in light of theforegoing description. Accordingly, it is intended to embrace all suchalternatives, modifications and variations as fall within the broadscope of the appended claims.

Thus, having described the invention, what is claimed is:

1. An articular surface replacement component sized and configured to beimplanted into an end of a first bone comprising: an exterior articularsurface defined by a convex head piece dimensioned to cover the end ofthe first bone; a plurality of scalloped anti-rotation bone grips on theconvex head piece for gripping the end of the first bone and allowingsolid fixation thereto; a centrally located stem extending from theconvex head piece; and a plurality of threads extending around the stem.2. The component of claim 1 wherein the articular surface replacementcomponent comprises a metatarsal component and the first bone comprisesa metatarsal bone.
 3. The component of claim 1 wherein the convex headpiece has a convex interior surface and a convex exterior surface. 4.The component of claim 3 wherein the convex interior and exteriorsurfaces have different radii providing a tapered head piece with athinnest portion residing at an outer periphery of the tapered headpiece.
 5. The component of claim 1 further including a centrally locateddriver hole on an exterior articular surface of the convex head piecefor inserting the first component into the first bone.
 6. The componentof claim 1 wherein the scalloped anti-rotation bone grips reside arounda peripheral edge of the convex head piece.
 7. The component of claim 1wherein the scalloped anti-rotation bone grips comprise scalloped edgesresiding along the peripheral edge of an interior side of the convexhead piece.
 8. The component of claim 1 wherein the scallopedanti-rotation bone grips are integrally formed with the convex headpiece.
 9. The component of claim 1 wherein the scalloped anti-rotationbone grips have angled edges.
 10. The component of claim 1 wherein thescalloped anti-rotation bone grips are non-serrated.
 11. The componentof claim 1 wherein the scalloped anti-rotation bone grips are serrated.12. The component of claim 11 wherein the serrated scallopedanti-rotation bone grips are angled.
 13. The component of claim 1wherein the scalloped anti-rotation bone grips reside on the convex headpiece to a depth ranging from 0.5 mm to 1 mm into an interior side ofthe convex head piece.
 14. The component of claim 1 further including aplurality of threads extending around the centrally located stem. 15.The component of claim 1 wherein the centrally located stem is tapered.16. The component of claim 1 wherein the centrally located stem has anon-threaded portion and a tapered threaded portion, the taperedthreaded portion having a length sufficient to extend through intactsub-chondral bone and into the first bone's medullary canal.
 17. Thecomponent of claim 1 wherein the component comprises a material selectedfrom the group consisting of titanium, a titanium alloy, stainless steeland a chromium alloy.
 18. The component of claim 1 further including atleast a portion of the component is coated with a subchondral bonereplacement in-growth coating.
 19. The component of claim 1 wherein theconvex head piece has an outer surface which forms a cartilaginousspherical articular surface and a coarsely finished interior surface forpromoting boney ingrowth and thereby facilitating fixation.
 20. Anarticular surface replacement component sized and configured to beimplanted into an end of a metatarsal bone comprising: an exteriorarticular surface defined by a convex head piece dimensioned to coverthe end of the metatarsal bone; a plurality of scalloped anti-rotationbone grips having angled edges integrally formed with and residingaround a peripheral edge of the convex head piece for gripping the endof the metatarsal bone and allowing solid fixation thereto; a centrallylocated stem extending from the convex head piece; and a plurality ofthreads extending around the stem.